Molecular characterization of hprt mutants induced by low- and high-LET radiations in human cells.
Southern blotting techniques were employed to examine the spectrum of molecular alterations in DNA induced by internally emitting iodine isotopes and X-rays at and around the hprt locus in a human lymphoblastoid cell line. We analyzed 165 mutant clones using a cDNA probe for the human hprt locus, and 3 anonymous sequence probes for regions of the X chromosome which are linked to hprt. The results were compared with those for 35 spontaneously arising mutant clones. The majority of ionizing radiation-induced mutants showed changes in the normal restriction patterns at the hprt locus, whereas very few alterations were seen at linked markers along the X chromosome. Total hprt coding sequence deletions comprised 30-48% of the changes observed at this locus, while partial deletions and rearrangements comprised 14-54% of the observed changes. In the case of mutants induced by [125I]dUrd, a densely ionizing radiation, the spectrum of alterations was dose-dependent; at low doses it was not significantly different from that seen after sparsely ionizing X-ray exposure, whereas a higher proportion of gene deletions and rearrangements occurred after high doses of this incorporated isotope. Changes were rarely observed in the 3 linked markers examined. Overall, these results indicate that the distribution of mutational events at the hprt locus in irradiated human cells may not only be LET-dependent but dose-dependent, and that deletions involving large regions of the X chromosome surrounding the hprt locus are rare events.
Whaley
J M
JM
Department of Cancer Biology, Harvard School of Public Health, Boston, MA 02115.
Little
J B
JB
D000818:Animals; D015139:Blotting, Southern; D002872:Chromosome Deletion; D015342:DNA Probes; D004307:Dose-Response Relationship, Radiation; D004735:Energy Transfer; D008040:Genetic Linkage; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D009154:Mutation; D011833:Radiation Injuries, Experimental / Q000235:genetics*; D014965:X-Rays
D015342:DNA Probes; D007457:Iodine Radioisotopes; D007041:Hypoxanthine Phosphoribosyltransferase